1. Background of the Invention
The invention relates generally to the enhanced removal of aerosols, such as fine liquid droplets and particulate matter, from a gas stream. More specifically, the invention is directed to the removal of aerosols, and in some embodiments additionally a vapor phase contaminant, from the flue gas of a combustion system.
2. Description of Related Art
The emission of aerosols, such as particulate matter or fly ash and acid mist, from flue gas generated by utility power plants is an important issue. Several technologies have been used to remove such aerosols from the flue gas before its release to the atmosphere, including wet and dry electrostatic precipitators, wet and dry scrubbers, and baghouses. However, these existing collectors are required to handle even higher amounts of aerosols as more materials such as sorbents for mercury and acid gas control are being intentionally injected into the flue gas stream and because new pollution control devices, such as selective reduction (SCR) catalysts, increase sulfuric acid mist formation in the flue gas. Otherwise, such increased aerosol loadings lead to increased particulate and acid mist emissions at the stack. In addition, environmental regulations are becoming increasingly more stringent, requiring power plants to reduce stack aerosol emissions even further. Therefore, it is desirable to improve and enhance the methods and equipment currently used for removing aerosols, including particulate matter or fly ash and acid mists, from gas streams. In particular, there is a need for methods and apparatuses or “polishers” that supplement the removal of particulate matter or fly ash obtained using traditional equipment.
Further, special attention has been given the emissions of vaporous trace contaminants, such as mercury (Hg), in flue gas generated by utility power plants and the impact such trace contaminants may have on the environment. Generally, trace contaminants include those vaporous chemical species present in relatively low concentrations in a given gas stream. For example, mercury is present in flue gas from a fossil-fuel-fired combustion system in very low concentrations (<1 ppm) and is present in a number of volatile compounds that are difficult to remove. Specially designed and costly emissions-control systems are required to effectively capture these trace amounts of mercury. Therefore, there is also a need to improve the methods and equipment used for removing such vaporous trace contaminants from gas streams.